Which chip you're looking for depends on what kind of car you have. The best way to find information is probably to seek out an enthuiast forum on the net - one is pretty much guaranteed to exist for your car, whether it's a old Firebird, Ford Probe, or Nissan Skyline. They'll have the info on what chips, replacements, piggybacks, or reflashes exist (and how they respectively perform). Whether or not they'll void your warranty is a tricky question. The phrase you'll hear bandied about is the "Maggnuson-Moss Warranty Act," which basically states that a manufacturer cannot void your warranty because of aftermarket parts unless they can prove the aftermarket parts caused the failure. Now, you're probably wondering what is meant by "prove," and therein lies the problem. Whether or not you can get warranty work done with an aftermarket ECU installed varies from manufacturer to manufacturer and even dealer to dealer. A lot of times, the manufacturer will simply deny you warranty service on the assumption that you won't sue, and they'll win that bet 99% of the time. If you mod your car, you're best off assuming your warranty is voided, but by al means do not volunteer any information when you bring it in for service.